During the life of a well a time can come when a lateral needs to be drilled to enhance production from a production from a producing zone or to penetrate a different zone. Since production tubing is in the well when the lateral needs to be drilled after a window is formed, it was deemed advantageous to be able to run a whipstock through the production tubing and anchor it in the larger casing. A milling assembly that also fit through tubing could also then be introduced to produce the window. Through tubing retrievable whipstocks were developed for this purpose and an illustrative one is U.S. Pat. No. 5,909,770.
However, in the past there were limits to this technique. It was used when the size of the tubing inside diameter was not substantially smaller than the inside diameter of the surrounding tubular, generally casing. The concern that remained unresolved in the past that limited the application of through tubing window milling is that in applications with greater ratios of tubing inside diameter to casing inside diameter the size of the through tubing whipstock that fit through tubing would leave large gaps on either side of the much larger surrounding casing so that the advancing mill could literally run off the sides of the whipstock or miss the whipstock ramp totally. If this happened the window or exit would be oriented incorrectly for the desired lateral to be later drilled. One way this situation was avoided was to pull all the production tubing and go in with a full sized whipstock, cut the window, drill the well to depth and then complete the well with the necessary completion equipment. Clearly, this required a lot of time and created a substantial cost. The problem was that no other alternatives were known.
The present invention is directed toward a solution. It provides a centralizer that can be inserted through tubing and subsequently expanded so that it is anchored and has a central passage larger than its run in outside diameter. Since the percent expansion of the centralizer is well above 30% beyond its run in dimension, the centralizer is configured to make such dramatic dimension changes while retaining the structural strength to guide a mill to track a whipstock ramp without going off one side or the other. The centralizer can be a cylinder that is slotted or alternatively a design with energized cantilevered fingers that can be allowed to spring out when the centralizer is properly placed. If a cylinder is used its opposed ends can be expanded for fixation leaving a smaller dimension in between for guidance of a mill.
Techniques for tubular expansion involving a high degree of expansion are illustrated in U.S. Pat. No. 6,896,052. Techniques involving performing a tubular and then using expansion to return it to its original shape which is larger than its run in dimension are illustrated in U.S. Pat. No. 5,785,120. Tubular screens have also been expanded downhole, as illustrated in U.S. Pat. No. 6,863,131.
Those skilled in the art will appreciate the various aspects of the present invention from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be found in the attached claims.